THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP98/04731.
The present invention relates to a color-difference signal conversion circuit to be employed in a television receiver which can reproduce a component video input signal based on various television systems in addition to a signal based on existing television systems, and in particular to a color-difference signal conversion circuit which can automatically convert, depending on various television systems, the above-mentioned component video input signal into a color-difference signal which is faithful to the colorimetry standard of the input signal. It relates more specifically to a technique that utilizes a functional relationship between transmitted chrominance signals PB and PR and color-difference signals B-Y and R-Y of an external component video input signal.
FIG. 4 shows an example of schematic structure of an existing television receiver. In FIG. 4, numeral 1 is an input circuit for a luminance signal Y and transmitted chrominance signals PB and PR of an external component video input signal. Numeral 2 is a demodulator for color-difference signal of an existing television system (hereinafter NTSC) to demodulate color-difference signals B-Y and R-Y from a luminance signal Y and a chrominance signal C of an NTSC television signal. Numeral 3 is first selector for manually selecting from either Y, PB, and PR signals of an external component video input signal or Y, B-Y, and R-Y signals of an NTSC signal. Numeral 4 is a sync separator to separate horizontal and vertical sync signals from a Y signal. Numeral 5 is a matrix circuit which has a function of converting incoming external component video input signals Y, PB, and PR of HDTV (High Definition TV) into HDTV primary color signals R, G, and B (the function hereinafter called xe2x80x9cHD matrix conversion functionxe2x80x9d), and a function of converting incoming NTSC signals Y, B-Y, and R-Y into NTSC primary color signals R, G, and B (the function hereinafter called xe2x80x9cSD matrix conversion functionxe2x80x9d). The operation of the matrix circuit is described below.
In FIG. 4, external component video input signals Y, PB, and PR are fed to the Y, PB, PR input circuit 1, and are transmitted to the first selector 3.
On the other hand, an NTSC luminance signal Y and a chrominance signal C are demodulated to Y, B-Y, and R-Y signals by the NTSC color-difference signal demodulator 2 and are transmitted to the first selector 3. Either one of the Y signal of an external component video input signal or the Y signal of an NTSC signal is selected by the first selector 3, and is transmitted to the sync separator 4. Horizontal and vertical sync signals separated from the Y signal by the sync separator 4 are transmitted to a deflection circuit. Also, either set of the Y, PB, and PR signals of the external component video input signal or set of the Y, B-Y, and R-Y signals of the NTSC signal is selected by the first selector 3, and is transmitted to the matrix circuit 5. When Y, PB, and PR signals have been transmitted, they are converted into HDTV primary color signals R, G, and B by the HD matrix conversion function and transmitted to a CRT drive circuit, whereas when Y, B-Y, and R-Y signals have been transmitted, they are converted into NTSC primary color signals R, G, and B by the SD matrix conversion function and transmitted to the CRT drive circuit.
However, the above-described conventional circuit structure has become unable to cope with digitalization of television broadcast or media convergence such as internet television broadcast. In Japan, although Hi-Vision (name of an HDTV system broadcast in Japan) has heretofore been the only available external component video input, in association with the advance of digitalization of television broadcast, there is recently a tendency of digital television signals based on various television systems being transmitted in the format of component video signals Y, PB, and PR through a single transmission channel. In the United States of America, 18 systems shown in FIG. 5 are being considered as digital television systems. A television system conforming to a colorimetry standard of SMPTE 274M is called HDTV, while a television system conforming to a colorimetry standard of SMPTE 170M is called SDTV. The colorimetry standard of NTSC system is SMPTE 170M. The colorimetry standard of Hi-Vision is SMPTE 274M. An SDTV signal transmitted in the format of Y, PB, and PR signals is transmitted to the matrix circuit 5 via the first selector 3, and is converted into primary color signals R, G, and B by the HDTV matrix conversion function rather than the SD matrix conversion function, thus presenting a problem of not being able to make a precise reproduction of colors.
Furthermore, as the media convergence proceeds in the future, there is a possibility of component video signals of personal computer image in the format of Y, PB, and PR being transmitted to television receivers through Internet, presenting a problem of how to discriminate the video signal formats in order to generate an adequate color-difference signal.
As data to characterize a video signal on which to discriminate its video signal format, the data shown in FIG. 6 and combinations of each of them may be noted, namely, horizontal sync frequency, vertical sync frequency, horizontal sync signal waveform, and number of scanning lines.
In order to address the above problems, the present invention has introduced into a television receiver a color-difference signal conversion circuit having features as described below. When an external component video input signal is an SDTV signal, the color-difference signal conversion circuit in accordance with the present invention converts its transmitted chrominance signals PB and PR into color-difference signals B-Y and R-Y. When an external component video input signal is an HDTV signal, transmitted chrominance signals PB and PR are directly fed to first selector. And the first selector supplies as its output either the above-mentioned transmitted chrominance signals PB and PR or color-difference signals B-Y and R-Y after automatically selecting them responding to a control signal properly supplied by a video signal discriminating circuit which discriminates the video signal format based on data characterizing a video signal such as the horizontal sync frequency, vertical sync frequency, horizontal sync signal waveform, and number of scanning lines, etc., of the external component video input signal. As a result, the television receiver can reproduce a color faithful to the colorimetry standard of the above-mentioned input signal.
The invention described in claim 1 of the present invention is an invention in which, in a television receiver comprising:
a Y, PB, PR input circuit for an external component video input signal comprising luminance signal Y and transmitted chrominance signals PB and PR;
an NTSC color-difference signal demodulator to demodulate color-difference signals B-Y and R-Y from luminance signal Y and chrominance signal C of an NTSC signal;
a sync separator to extract horizontal and vertical sync signals from the Y signal;
a first selector to select from either an output signal from the NTSC color-difference signal demodulator or an output signal from the Y, PB, PR input circuit for an external component video input signal, and to supply the selected output to a matrix circuit;
and a matrix circuit having a function (HD matrix conversion function) of converting Y, PB, and PR signals into HDTV primary color signals R, G, and B when HDTV signals Y, PB, and PR conforming to the HDTV colorimetry standard have been transmitted, and a function (SD matrix conversion function) of converting Y, B-Y, and R-Y signals into SDTV primary color signals R, G, and B when SDTV signals Y, B-Y, and R-Y have been transmitted,
a color-difference signal conversion circuit inserted between the Y, PB, PR input circuit and the first selector and mutually connected in series, and characterized by comprising:
a video signal discriminating circuit which determines the video signal format based on data extracted from the horizontal sync signal and the vertical sync signal and characterizing a video signal, and generates a control signal to make an amplitude conversion circuit generate a signal optimum for the colorimetry standard of the input signal;
and an amplitude conversion circuit which automatically converts amplitudes of the Y, PB, and PR signals supplied by the Y, PB, PR input circuit responding to the control signal generated by the video signal discriminating circuit, and generates a signal to reproduce a color faithful to the colorimetry standard of the input signal; is incorporated,
and the color-difference signal conversion circuit is capable of reproducing a color faithful to the colorimetry standard of the input signal as it automatically converts the amplitudes of Y, PB, and PR as supplied by the Y, PB, PR input circuit depending on the video signal format of the Y, PB, PR input signal, and supplies its output to the matrix circuit.